1. Field of the Invention
The invention relates to the field of the blocking of peripheral nerves, for example the field of plexus anaesthesia, and especially to an injection device having an injection needle of metal which has at one end a base for the attachment of a syringe, and at the opposite end an especially shaped needle tip.
2. State of the Art
Plexus blocks are used in anaesthesia in operations on the arm and hand, for example, especially when urgent operations must be performed on patients who are not fasting. In spite of undisputed advantages, plexus blocks with so-called immobile needles have been successfully practiced only in exceptional cases and by very experienced anaesthetists, since the tip of the injection needle or cannula has, under certain circumstances, caused severe injuries to the nerve fibers and blood vessels as well as degenerative changes in and discontinuities of the fibers.
Conventional injection needles usually have a tip which is defined by a cylindrical circumferential surface and a surface made by grinding at an angle of less than 20.degree. to the cannula axis. The inventor has found through tests that the main reason for lesions to nerve fibers and blood vessels in plexus anaesthesia using the known injection needles is that the needles have very sharp tips. Such sharp needle tips "skewer" even thin nerve fibers and blood vessels instead of turning them aside.